1. Field of the Invention
The present invention relates generally to press tipping moment monitoring and, more particularly, to a method of generating a tipping moment severity chart for the determination of die long-term operating reliability during production operation and to an apparatus utilizing the information generated by the above method in monitoring press tipping moment severity and die life risk condition based upon tipping moment severity so that die reliability may be determined.
2. Description of the Related Art
Conventional press machines employ a tooling apparatus in the form of a die assembly to shape a workpiece, such as in a stamping or drawing operation. The die assembly particularly includes a lower die attached to a non-moveable bed or bolster and an upper die or punch attached to a reciprocating slide. The upper and lower dies, which are installed in opposing spaced apart relation to one another, cooperate during press machine operation to mutually engage the workpiece at respective sides thereof to thereby effect the desired forming activity.
Repeated stamping operations of a mechanical press cause die wear. The ability to accurately predict die wear or to predict operating conditions which indicate the propensity for increased die wear is advantageous in that press down time for die replacement or reconditioning can be predicted or even potentially diverted by proactive early corrective intervention. The ability to predict die wear allows the operator of a mechanical press to better plan times for die replacement or to intervene with corrective actions, so that productivity loss is not experienced. Further, the ability to predict die wear is advantageous in that press down time associated with die maintenance can be minimized. The desire to predict die wear has led press users to monitor press load and to use this monitored load as a loosely related predictor of potential die wear.
The ability to predict die wear based upon applied load does not provide an accurate indication of die wear. To accurately predict die wear, tipping moment severity also must be accounted for. Currently, a press user cannot accurately predict die wear so that losses in productivity due to excessive or insufficient die maintenance can be avoided. Additionally, load sensors of the current die wear predictive systems do not account for die chipping due to tipping moments. Die chipping due to tipping moments in a mechanical press leads to inferior production quality and associated production losses.
The present invention is directed to improve upon the aforementioned mechanical press die wear predictive systems wherein it is desired to monitor the tipping moment of any specific press/die application while it is operating to accurately predict die wear and to avoid die chipping due to tipping moments.
The present invention provides a method and apparatus for predicting conditions creating increased die wear which is developed by tipping moments experienced in the mechanical press.
The invention, in one form thereof, comprises a load sensor attached to the bed of a running press and a computational device for receiving the load value from the load sensor and computing a measure of tipping moment severity of the running press based upon the sensed load value and methods for computing moments. The computational device can be, for example, a microprocessor.
The invention, in another form thereof, includes one or more load sensors attached to the bed of a running press and a computational device which stores a unique tipping moment severity chart for the running press, a plurality of tipping moment severity factors which correspond to zones of tipping moment severity on the tipping moment severity chart and a plurality of zone of criticality factors which correspond to the zones of criticality on the tipping moment severity chart. The computational device receives the load values sensed from the load sensors and uses means to compute tipping moments based upon the sensed load values.
The invention, in another form thereof, includes one or more load sensors attached to the bed of a running press and a computational device which stores a unique tipping moment severity chart for the running press, a plurality of tipping moment severity factors which correspond to zones of tipping moment severity on the tipping moment severity chart and a plurality of zone of criticality factors which correspond to the zones of criticality on the tipping moment severity chart. The computational device receives the load values sensed from the load sensors and uses means to compute tipping moments based upon the sensed load values. The computational device also utilizes the tipping moment severity chart, the tipping moment severity factors, the zone of criticality factors, and the measured tipping moment to compute a measure of die life risk condition.
The invention, in another form thereof, includes one or more load sensors attached to the bed of a running press and a computational device which stores a unique tipping moment severity chart for the running press, a plurality of tipping moment severity factors which correspond to zones of tipping moment severity on the tipping moment severity chart and a plurality of zone of criticality factors which correspond to the zones of criticality on the tipping moment severity chart. The computational device receives the load values sensed from the load sensors and uses means to compute tipping moments based upon the sensed load values. The computational device utilizes the tipping moment severity chart, the tipping moment severity factors, the zone of criticality factors, and the measured tipping moment to compute a measure of die life risk condition. The values computed in the computational device, including tipping moment severity and die life risk condition may be communicated to, for example, a digital storage device, a modem, a display device, an alert device or a shutoff device. The digital storage device may be utilized for compiling histories of tipping moment severity and die life risk condition. A modem or other communication network such as the Internet may be used for communicating tipping moment severity and/or die life risk condition to a remote location. The display device may display tipping moment and/or die life risk condition so that service, maintenance, or production personnel may determine how changing press speed, shut height and die changes can alter the expected life span of the die and punch set. The alert device and the shutoff device will produce an alert signal and discontinue press operation, respectively, if the tipping moment severity and/or die life risk condition exceeds a predetermined measure.
The invention, in another form thereof, comprises a method of monitoring the die reliability condition of a running press by monitoring the tipping moment severity of the running press.
The invention, in another form thereof, comprises a method of monitoring the die reliability condition of a running press which includes: placing at least one load sensor on the bed of a running press, providing a computational device, communicating the load sensed by the load sensor to the computational device, and computing the tipping moment severity of the press using the sensed load value.
The invention, in another form thereof, comprises a method of computing a unique tipping moment severity chart for a particular press and die set. This method includes the steps of: dividing the ordinate of a tipping moment severity versus slide vertical position graph into a plurality of zones which zones represent different tipping moment severity levels, plotting the slide vertical motion on the tipping moment severity chart, dividing the ordinate of the tipping moment severity versus slide vertical position graph into a plurality of zones of criticality representing different phases of punch travel, projecting the zones of criticality onto the plot of slide vertical motion and projecting the zones of criticality from the plot of slide vertical motion to the abscissa of the tipping moment severity versus slide vertical position graph.
The invention, in another form thereof, comprises a method of generating a unique tipping moment severity chart for a particular press and die set. This method includes the steps of: dividing the ordinate of a tipping moment severity versus slide vertical position graph into a plurality of zones which zones represent different tipping moment severity levels; plotting the slide vertical motion on the tipping moment severity chart; dividing the ordinate of the tipping moment severity versus slide vertical position graph into three zones of criticality which represent free punch travel, punch travel through the stock material and punch travel through the die; projecting the zones of criticality onto the plot of slide vertical motion and projecting the zones of criticality from the plot of slide vertical motion to the abscissa of the tipping moment severity versus slide vertical position graph.
The invention, in another form thereof, comprises a method of generating a unique tipping moment severity chart for a particular press and die set. This method includes the steps of: dividing the positive portion of the ordinate of a tipping moment severity versus slide vertical position graph into four zones of tipping moment severity, dividing the negative portion of the ordinate of a tipping moment severity versus slide vertical position graph into four zones of tipping moment severity, plotting the slide vertical motion on the tipping moment severity chart, dividing the ordinate of the tipping moment severity versus slide vertical position graph into a plurality of zones of criticality which represent different phases of punch travel, projecting the zones of criticality onto the plot of slide vertical motion and projecting the zones of criticality from the plot of slide vertical motion to the abscissa of versus tipping moment severity versus the slide vertical position graph.
The invention, in another form thereof, comprises a method of monitoring the die life risk condition of a mechanical press. This method includes the steps of: monitoring the tipping moment severity of the press application, generating a unique tipping moment severity chart for the press application, plotting the monitored tipping moment severity of the press on the unique tipping moment severity chart for the press and computing the die life risk condition of the press.
The invention, in another form thereof, comprises a method of monitoring the die life risk condition of a mechanical press. This method includes the steps of: monitoring the tipping moment severity of the press; generating a unique tipping moment severity chart for the press; plotting the monitored tipping moment severity of the press on the unique tipping moment severity chart for the press; determining the duration of the positive peak tipping moment severity level; determining the duration of the negative peak tipping moment severity level; determining the tipping moment severity factor associated with the positive peak tipping moment severity level; determining the tipping moment severity factor associated with the negative peak tipping moment severity level; determining the zone of criticality factor associated with the positive peak tipping moment severity level; determining the zone of criticality factor associated with the negative peak tipping moment severity level; computing a die life risk condition component value associated with the positive peak tipping moment severity level using the duration of the positive peak tipping moment severity, the tipping moment severity factor associated with the positive peak tipping moment severity and the zone of criticality factor associated with the positive peak tipping moment severity level; computing a die life risk condition component value associated with the negative peak tipping moment severity level using the duration of the negative peak tipping moment severity, the tipping moment severity factor associated with the negative peak tipping moment severity and the zone of criticality factor associated with the negative peak tipping moment severity level; and computing a die life risk condition of the press by summing the die life risk condition component value associated with the positive peak tipping moment severity level and the die life risk condition component value associated with the negative peak tipping moment severity level.
The invention, in another form thereof, comprises a method of monitoring the die life risk condition of a mechanical press. This method includes the steps of: monitoring the tipping moment severity of the press; generating a unique tipping moment severity chart for the press; plotting the monitored tipping moment severity of the press on the unique tipping moment severity chart for the press; determining the duration of the positive peak tipping moment severity level; determining the duration of the negative peak tipping moment severity level; determining the tipping moment severity factor associated with the positive peak tipping moment severity level; determining the tipping moment severity factor associated with the negative peak tipping moment severity level; determining the zone of criticality factor associated with the positive peak tipping moment severity level; determining the zone of criticality factor associated with the negative peak tipping moment severity level; computing a die life risk condition component value associated with the positive peak tipping moment severity level using the positive peak tipping moment severity, the duration of the positive peak tipping moment severity, the tipping moment severity factor associated with the positive peak tipping moment severity and the zone of criticality factor associated with the positive peak tipping moment severity level; computing a die life risk condition component value associated with the negative peak tipping moment severity level using the negative peak tipping moment severity, the duration of the negative peak tipping moment severity, the tipping moment severity factor associated with the negative peak tipping moment severity and the zone of criticality factor associated with the negative peak tipping moment severity level; and computing a die life risk condition of the press by summing the die life risk condition component value associated with the positive peak tipping moment severity level and the die life risk condition component value associated with the negative peak tipping moment severity level.
The invention, in another form thereof, comprises a method of monitoring the die life risk condition of a mechanical press. This method includes the steps of: monitoring the tipping moment severity of the press, generating a unique tipping moment severity chart versus zone of criticality for the press, plotting the monitored tipping moment severity of the press on the unique tipping moment severity chart for the press, determining the tipping moment severity factor associated with the positive peak tipping moment severity level, determining the tipping moment severity factor associated with the negative peak tipping moment severity level, determining the zone of criticality factor associated with the positive peak tipping moment severity level, determining the zone of criticality factor associated with the negative peak tipping moment severity level, computing a die life risk condition component value associated with the positive peak tipping moment severity level using the tipping moment severity factor associated with the positive peak tipping moment severity level and the zone of criticality factor associated with the positive peak tipping moment severity level, computing a die life risk condition component value associated with the negative peak tipping moment severity level using the tipping moment severity factor associated with the negative peak tipping moment severity and the zone of criticality factor associated with the negative peak tipping moment severity level; and computing a die life risk condition of the press by summing the die life risk condition component value associated with the positive peak tipping moment severity level and the die life risk condition component value associated with the negative peak tipping moment severity level.
The invention, in another form thereof, comprises a method of monitoring the die life risk condition of a mechanical press. This method includes the steps of: monitoring the tipping moment severity of the press; generating a unique tipping moment severity chart for the press; plotting the monitored tipping moment severity of the press on the unique tipping moment severity chart for the press; associating the monitored tipping moment severity with the appropriate zone of criticality factor; computing the absolute value of the monitored tipping moment severity; computing a weighted tipping moment severity value using the absolute value of the monitored tipping moment severity and the zone of criticality factor associated with the monitored tipping moment severity; recording weighted tipping moment severity values versus time; and generating a cumulative tipping moment severity value for one slide stroke using the weighted tipping moment severity values versus time.
The invention, in another form thereof, comprises a method of monitoring the die life risk condition of a mechanical press. This method includes the steps of: monitoring the tipping moment severity of the press; generating a unique tipping moment severity chart for the press; plotting the monitored tipping moment severity of the press on the unique tipping moment severity chart for the press; associating the monitored tipping moment severity with the appropriate zone of criticality factor; computing the absolute value of the monitored tipping moment severity; computing a weighted tipping moment severity value using the absolute value of the monitored tipping moment severity, and the zone of criticality factor associated with the monitored tipping moment severity; recording weighted tipping moment severity values versus time; and generating a cumulative tipping moment severity value for one slide stroke using the weighted tipping moment severity values versus time. Multiple peaks of tipping moment severity are accounted for when utilizing measures of die life risk condition based upon cumulative tipping moment severity for a slide stroke.
An advantage of the present invention is that constant monitoring of the tipping moment severity of a press allows the tool design to be changed to reduce tipping moments and to increase the parallelism of the press thereby increasing the produced part quality.
Another advantage of the present invention is that the propensity for increased die wear may be accurately predicted so that press down time for die replacement or reconditioning can be predicted and die replacement or reconditioning can be planned so that lost productivity is not experienced.
Another advantage of the present invention is that die wear may be accurately predicted so that losses in productivity due to excessive or insufficient die maintenance can be avoided.
A further advantage of the present invention is that by monitoring tipping moment severity, die chipping due to tipping moments in a mechanical press can be eliminated or greatly improved so that the inferior production quality and the associated productivity losses due to die chipping can be eliminated.